Effect of Mixed Anions - (SO42- - ClO4- ) and (SO42- - NO3-) on Fe0 Reactivity

Pump-and-treat (P&T) based methods of groundwater remediation have been found to be costly and inefficient where many organics pollutants are concerned.  Granular iron permeable reactive barriers (GIPRBs) are an ideal alternative to P&T based methods because they are implemented sub-surface and are designed to behave as passive groundwater remediation systems.  However, factors such as groundwater geochemistry need to be considered when selecting specific sites for the application of GIPRBs, since geochemistry can affect short and long-term performance. In this work, batch experiments were conducted to observe the effects of sulfate (SO₄^2-), perchlorate (ClO₄^-), and nitrate (NO₃^-) (all anions commonly present in groundwater) on the reactivity of granular iron (Fe⁰). The reactivity of the granular iron surface can be assessed by measuring the reduction rate of 4-chloronitrobenzene (4ClNB) as a function of initial 4ClNB concentration and anion type.  Solutions of mixed anions, (SO₄^2-) with (ClO₄^-) and (SO₄^2-) with (NO₃^-), were prepared with an ionic strength of 8 mM and then adjusted to pH 10 for all experiments.  These solutions were spiked with 4ClNB in glass-encased magnetic reactors (GEMs) containing ~2.5 g of granular iron. According to the findings of this study, perchlorate (ClO₄^-) has no effect on the reactivity of granular iron (Fe⁰), sulfate (SO₄^2-) is known to increase the reactivity of granular iron (Fe⁰) toward 4ClNB, and nitrate (NO₃^-) inhibits the reactivity of granular iron toward 4CLNB.